Special emphasis on the effect of the AMV associated endonuclease on primer tRNA Trp. Preliminary results indicate the endonuclease generates a 16 nucleotide fragment from the 3'-end of tRNA Trp. This region (3'-end) has been shown to be critical to base pairing to the viral 35S RNA and acts as the 3'-OH primer region. Biophysical studies are planned to determine if AMV DNA polymerase plays an active role in melting the CCA stem as a prerequisite for priming. The cloning of the large viral double stranded AMV DNA. Subsequent characterization of the pBr322 hybrids to characterize the cloned DNA. All cloning experiments are to be carried in collaboration with Dr. Takis Papas of NCI.